Systems and methods for using electrical asymmetry effect to control plasma process space in semiconductor fabrication

ABSTRACT

Systems and methods are disclosed for plasma enabled film deposition on a wafer in which a plasma is generated using radiofrequency signals of multiple frequencies and in which a phase angle relationship is controlled between the radiofrequency signals of multiple frequencies. In the system, a pedestal is provided to support the wafer. A plasma generation region is formed above the pedestal. An electrode is disposed in proximity to the plasma generation region to provide for transmission of radiofrequency signals into the plasma generation region. A radiofrequency power supply provides multiple radiofrequency signals of different frequencies to the electrode. A lowest of the different frequencies is a base frequency, and each of the different frequencies that is greater than the base frequency is an even harmonic of the base frequency. The radiofrequency power supply provides for variable control of the phase angle relationship between each of the multiple radiofrequency signals.

BACKGROUND

1. Field of the Invention

The present invention relates to semiconductor device fabrication.

2. Description of the Related Art

Many modern semiconductor chip fabrication processes include generationof a plasma from which ions and/or radical constituents are derived foruse in either directly or indirectly affecting a change on a surface ofa wafer exposed to the plasma. For example, various plasma-basedprocesses can be used to etch material from a wafer surface, depositmaterial onto a wafer surface, or modify a material already present on awafer surface. The plasma is often generated by applying radiofrequency(RF) power to a process gas in a controlled environment, such that theprocess gas becomes energized and transforms into the desired plasma.The characteristics of the plasma are affected by many processparameters including, but not limited to, material composition of theprocess gas, flow rate of the process gas, geometric features of theplasma generation region and surrounding structures, pressure within theplasma generation region, temperatures of the process gas andsurrounding materials, frequency and magnitude of the RF power applied,and bias voltage applied to attract charged constituents of the plasmatoward the wafer, among others.

However, in some plasma processes, the above-mentioned processparameters may not provide for adequate control of all plasmacharacteristics and behavior. In particular, in some plasma processes,an instability referred to as a “plasmoid” may occur within the plasma,where the plasmoid is characterized by a small area of higher densityplasma surrounded by larger volumes of normal density plasma. Theformation of plasmoids can lead to non-uniformity in the processingresults on the wafer. Therefore, it is of interest to mitigate and/orcontrol plasmoid formation within a plasma process without adverselyimpacting performance of the plasma process. It is within this contextthat the present invention arises.

SUMMARY

In an example embodiment, a method is disclosed for performing a plasmaprocess to deposit a film on a wafer. The method includes positioningthe wafer on a top surface of a pedestal in exposure to a plasmageneration region. The method also includes supplying a process gascomposition to the plasma generation region. The process gas compositionincludes oxygen and at least one bombardment gas. The method alsoincludes generating radiofrequency signals of at least two differentfrequencies, where a lowest of the at least two different frequencies isa base frequency, and where each radiofrequency signal having afrequency greater than the base frequency is in an even harmonicrelationship with the radiofrequency signal of the base frequency, andwhere each radiofrequency signal having a frequency greater than thebase frequency is in a fixed phase relationship with the radiofrequencysignal of the base frequency. The method also includes supplying thegenerated radiofrequency signals to an electrode for transmission intothe plasma generation region so that the radiofrequency signalstransform the process gas composition into a plasma within the plasmageneration region, with the plasma causing deposition of the film on thewafer. The method also includes adjusting a phase angle relationshipbetween radiofrequency signals of each of the at least two differentfrequencies to control a parameter of the film deposited on the wafer.

In an example embodiment, a system is disclosed for performing a plasmaprocess to deposit a film on a wafer. The system includes a pedestalhaving a top surface configured to support the wafer. The system alsoincludes a plasma generation region formed above the top surface of thepedestal. The system also includes a process gas supply configured tosupply a process gas composition to the plasma generation region. Theprocess gas composition includes oxygen and at least one bombardmentgas. The system also includes an electrode disposed in proximity to theplasma generation region to provide for transmission of radiofrequencysignals from the electrode into the plasma generation region. The systemalso includes a radiofrequency power supply configured to simultaneouslysupply multiple radiofrequency signals of different frequencies to theelectrode, where a lowest of the different frequencies is a basefrequency, and where each radiofrequency signal having a frequencygreater than the base frequency is in an even harmonic relationship withthe radiofrequency signal of the base frequency, and where eachradiofrequency signal having a frequency greater than the base frequencyis in a fixed phase relationship with the radiofrequency signal of thebase frequency. The multiple radiofrequency signals have respectivefrequencies set to transform the process gas composition into the plasmawithin the plasma generation region to cause deposition of the film onthe wafer. The radiofrequency power supply also includes a phasecontroller configured to provide for variable control of a phase anglerelationship between each of the multiple radiofrequency signals, whereadjustment of the phase angle relationship is used to control aparameter of the film deposited on the wafer.

Other aspects and advantages of the invention will become more apparentfrom the following detailed description, taken in conjunction with theaccompanying drawings, illustrating by way of example the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a wafer processing system configured to perform aplasma enhanced film deposition process on a wafer, in accordance withsome embodiments of the present invention.

FIG. 1B illustrates a wafer processing system that is configured toperform an atomic layer deposition (ALD) process on the wafer (e.g. anALD oxide process), in accordance with some embodiments of the presentinvention.

FIG. 2 shows a top view of a multi-station processing tool that includesfour processing stations, in accordance with some embodiments of thepresent invention.

FIG. 3 shows a schematic view of an embodiment of the multi-stationprocessing tool interfaced with an inbound load lock and an outboundload lock, in accordance with some embodiments of the present invention.

FIG. 4 shows an example of the pedestal configured to receive the waferfor a deposition process, such as an atomic layer deposition (ALD)process, in accordance with some embodiments of the present invention.

FIG. 5 shows a plasma processing system configured to implementelectrical asymmetry effect (EAE) control to provide for separatemodulation of ion energy flux and peak ion energy in order to controlvariations in film deposition results caused by plasma ion behavior, inaccordance with some embodiments of the present invention.

FIG. 6 shows another plasma processing system configured to implementEAE control to provide for separate modulation of ion energy flux andpeak ion energy in order to control variations in film depositionresults caused by plasma ion behavior, in accordance with someembodiments of the present invention.

FIG. 7 shows another plasma processing system configured to implementEAE control to provide for separate modulation of ion energy flux andpeak ion energy in order to control variations in film depositionresults caused by plasma ion behavior, in accordance with someembodiments of the present invention.

FIG. 8 shows plots of deposited film thickness profile across the wafercorresponding to use of the EAE phase angle relationship of about 10°and corresponding to use of the EAE phase angle relationship of about55°, in accordance with some embodiments of the present invention.

FIG. 9 shows a flowchart of a method for performing a plasma process todeposit a film on a wafer, in accordance with some embodiments of thepresent invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be apparent, however, to one skilled in the art that the presentinvention may be practiced without some or all of these specificdetails. In other instances, well known process operations have not beendescribed in detail in order not to unnecessarily obscure the presentinvention.

Deposition of films on a semiconductor wafer can be accomplished using aplasma enhanced chemical vapor deposition (PECVD) process and/or aplasma enhanced atomic layer deposition (PEALD) process. The system usedin the PECVD and PEALD processes may take many different forms. Forexample, the system can include one or more chambers or “reactors”(sometimes including multiple stations) that house one or more wafersand are suitable for wafer processing. Each chamber may house one ormore wafers for processing. The one or more chambers maintain the waferin a defined position or positions (with or without motion within thatposition, e.g., rotation, vibration, or other agitation). A waferundergoing deposition may be transferred from one station to anotherwithin a reactor chamber during the process. Of course, the filmdeposition may occur entirely at a single station or any fraction of thefilm may be deposited at any number of stations. While in process, eachwafer is held in place by a pedestal, wafer chuck, and/or other waferholding apparatus. For certain operations, the apparatus may include aheater such as a heating plate to heat the wafer.

In an example embodiment, the term wafer as used herein refers to asemiconductor wafer. Also, in various embodiments, the wafer as referredto herein may vary in form, shape, and/or size. For example, in someembodiments, the wafer as referred to herein may correspond to a 200 mm(millimeters) semiconductor wafer, a 300 mm semiconductor wafer, or a450 mm semiconductor wafer. Also, in some embodiments, the wafer asreferred to herein may correspond to a non-circular substrate, such as arectangular substrate for a flat panel display, or the like, among othershapes.

FIG. 1A illustrates a wafer processing system 100 configured to performa plasma enhanced film deposition process on a wafer 101, in accordancewith some embodiments of the present invention. The system includes achamber 102 having a lower chamber portion 102 b and an upper chamberportion 102 a. A center column 141 is configured to support a pedestal140 formed of an electrically conductive material. The electricallyconductive pedestal 140 is connected to receive RF signals from an RFpower supply 104 by way of a match network 106, depending on a settingof an RF direction control module 250. Also, in the wafer processingsystem 100 of FIG. 1A, a showerhead electrode 150 is configured andconnected to receive RF signals from the RF power supply 104 by way ofthe match network 106, depending on the setting of the RF directioncontrol module 250. In some embodiments, the RF direction control module250 is configured to direct RF signals transmitted from the RF powersupply 104 by way of the match network 106 to either the showerheadelectrode 150 or to the pedestal 140. Also, the RF direction controlmodule 250 is configured to electrically connect whichever one of theshowerhead electrode 150 and the pedestal 140 that is not currentlyreceiving RF signals to a reference ground potential. In this manner, ata given time, the RF direction control module 250 operates to ensurethat either the showerhead electrode 150 will receive RF signals fromthe RF power supply 104 while the pedestal 140 is electrically connectedto the reference ground potential, or the pedestal 140 will receive RFsignals from the RF power supply 104 while the showerhead electrode 150is electrically connected to the reference ground potential.

The RF power supply 104 is controlled by a control module 110, e.g., acontroller. The control module 110 is configured to operate the waferprocessing system 100 by executing process input and controlinstructions/programs 108. The process input and controlinstructions/programs 108 may include process recipes, having directionsfor parameters such as power levels, timing parameters, process gases,mechanical movement of the wafer 101, etc., such as to deposit or formfilms over the wafer 101.

In some embodiments, the center column 141 can include lift pins, whichare controlled by lift pin control 122. The lift pins are used to raisethe wafer 101 from the pedestal 140 to allow an end-effector to pick upthe wafer 101, and to lower the wafer 101 after being placed by theend-effector. The wafer processing system 100 further includes a gassupply system 112 that is connected to process gas supplies 114, e.g.,gas chemistry supplies from a facility. Depending on the processingbeing performed, the control module 110 controls the delivery of processgases 114 via the gas supply system 112. The chosen process gases arethen flowed into the showerhead electrode 150 and distributed into aplasma processing region between the showerhead electrode 150 and thewafer 101 disposed upon the pedestal 140.

Further, the process gases may be premixed or not. Appropriate valvingand mass flow control mechanisms may be employed within the gas supplysystem 112 to ensure that the correct process gases are delivered duringthe deposition and plasma treatment phases of the process. Process gasesexit the plasma processing region and flow through an exhaust outlet143. A vacuum pump (such as a one or two stage mechanical dry pump,among other types) draws process gases out of the processing volume andmaintains a suitably low pressure within the processing volume by aclosed loop feedback controlled flow restriction device, such as athrottle valve or a pendulum valve.

Also shown is a carrier ring 200 that encircles an outer region of thepedestal 140. The carrier ring 200 is configured to support the wafer101 during transport of the wafer 101 to or from the pedestal 140. Thecarrier ring 200 is configured to sit over a carrier ring support regionthat is a step down from a wafer support region in the center of thepedestal 140. The carrier ring 200 has an annular shaped disc structureand includes an outer edge side of its disc structure, e.g., outerradius, and a wafer edge side of its disc structure, e.g., inner radius,that is closest to where the wafer 101 sits. The wafer edge side of thecarrier ring 200 includes a plurality of contact support structureswhich are configured to lift the wafer 101 when the carrier ring 200 islifted by spider forks 180. The carrier ring 200 is therefore liftedalong with the wafer 101 and can be rotated to another station, e.g., ina multi-station system. Carrier ring lift and/or rotate control signals124 are generated by the control module 110 to control operation of thespider forks 180 to lift and/or rotate the carrier ring 200.

FIG. 1B illustrates a wafer processing system 100A that is configured toperform an atomic layer deposition (ALD) process on the wafer 101 (e.g.an ALD oxide process), in accordance with some embodiments of thepresent invention. Similar componentry as described with regard to FIG.1A is shown in FIG. 1B. Specifically, the wafer processing system 100Aalso includes the upper chamber portion 102 a, the lower chamber portion102 b, the control module 110, the RF power supply 104, the matchnetwork 106, the carrier ring 200, and the spider forks 180. In thewafer processing system 100A, a pedestal 140A is configured to include adielectric body 251. In some embodiments, the pedestal 140A includes anelectrically conductive layer 509 disposed on a top surface of thedielectric body 251, with the wafer 101 disposed on the electricallyconductive layer 509. However, in some embodiments, the electricallyconductive layer 509 is not present, and the wafer 101 is disposeddirectly on the top surface of the dielectric body 251. In someembodiments, the dielectric body 251 is affixed directly to the column141. And, in some embodiments, the dielectric body 251 is supported by aconductive structure 252 that is affixed to the column 141.

In some embodiments, a heating component 253, such as a resistanceheating element, is disposed with the dielectric body 251 of thepedestal 140A. The heating component 253 is connected to a heater powersupply 255, which is in turn connected to the control module 110. Withthe heating component 253 present, in some embodiments, the heater powersupply 255 can be operated in accordance with a prescribed recipe asprovided by the process input and control instructions/programs 108 andas executed by the control module 110. It should also be understood thattemperature measurement devices can be installed on/within the pedestal140A and/or at other locations around the pedestal 140A to providetemperature measurement data to the control module 110, thereby enablingoperation of a closed-loop temperature feedback control circuit betweenthe control module 110 and the heater power supply 255.

The dielectric body 251 of the pedestal 140A includes an RF electrode254 configured and connected to receive RF signals from the RF powersupply 104 by way of the match network 106, depending on the setting ofan RF direction control module 250. Also, in the wafer processing system100A of FIG. 1B, a showerhead electrode 150A is configured and connectedto receive RF signals from the RF power supply 104 by way of the matchnetwork 106, depending on the setting of the RF direction control module250. In some embodiments, the RF direction control module 250 isconfigured to direct RF signals transmitted from the RF power supply 104by way of the match network 106 to either the showerhead electrode 150Aor to the RF electrode 254. Also, the RF direction control module 250 isconfigured to electrically connect whichever one of the showerheadelectrode 150A and the RF electrode 254 that is not currently receivingRF signals to a reference ground potential. In this manner, at a giventime, the RF direction control module 250 operates to ensure that eitherthe showerhead electrode 150A will receive RF signals from the RF powersupply 104 while the RF electrode 154 is electrically connected to thereference ground potential, or the RF electrode 154 will receive RFsignals from the RF power supply 104 while the showerhead electrode 150Ais electrically connected to the reference ground potential.

FIG. 2 shows a top view of a multi-station processing tool 300 thatincludes four processing stations, in accordance with some embodimentsof the present invention. This top view is of the lower chamber portion102 b (e.g., with the top chamber portion 102 a removed forillustration). The four processing stations are accessed by spider forks180. Each spider fork 180, or fork, includes a first and second arm,each of which is positioned around a portion of each side of thepedestal 140/140A. The spider forks 180, using an engagement androtation mechanism 220 are configured to raise up and lift the carrierrings 200 (i.e., from a lower surface of the carrier rings 200) from theprocessing stations in a simultaneous manner, and then rotate a distanceof at least one or more stations before lowering the carrier rings 200(where at least one of the carrier rings supports a wafer 101) so thatfurther plasma processing, treatment and/or film deposition can takeplace on respective wafers 101.

FIG. 3 shows a schematic view of an embodiment of the multi-stationprocessing tool 300 interfaced with an inbound load lock 302 and anoutbound load lock 304, in accordance with some embodiments of thepresent invention. A robot 306, at atmospheric pressure, is configuredto move wafers 101 from a cassette loaded through a pod 308 into inboundload lock 302 via an atmospheric port 310. Inbound load lock 302 iscoupled to a vacuum source/pump so that, when atmospheric port 310 isclosed, inbound load lock 302 may be pumped down. Inbound load lock 302also includes a chamber transport port 316 interfaced with processingchamber 102. Thus, when chamber transport 316 is opened, another robot312 may move the wafer from inbound load lock 302 to the pedestal140/140A of a first process station for processing.

The depicted processing chamber 102 comprises four process stations,numbered from 1 to 4 in the example embodiment shown in FIG. 3. In someembodiments, processing chamber 102 may be configured to maintain a lowpressure environment so that wafers may be transferred using the carrierring 200 among the process stations 1-4 without experiencing a vacuumbreak and/or air exposure. Each process station 1-4 depicted in FIG. 3includes a pedestal 140/140A and showerhead electrode 150/150A andassociated process gas supply connections. Also, it should be understoodthat in other embodiments the processing chamber 102 can include lessthan four process stations or more than four process stations.

FIG. 3 also shows the spider forks 180 for transferring wafers withinthe processing chamber 102. As mentioned above, the spider forks 180rotate and enable transfer of wafers from one processing station toanother. The transfer occurs by enabling the spider forks 180 to liftthe carrier rings 200 from an outer undersurface, which lifts the wafers101, and rotates the wafers 101 and carrier rings 200 together to thenext processing station. In one configuration, the spider forks 180 aremade from a ceramic material to withstand high levels of heat duringprocessing.

FIG. 4 shows an example of the pedestal 140/140A configured to receivethe wafer 101 for a deposition process, such as an atomic layerdeposition (ALD) process, in accordance with some embodiments of thepresent invention. In some embodiments, the pedestal 140/140A includesthe electrically conductive layer 509 positioned on a central topsurface of the pedestal 140/140A, where the central top surface isdefined by a circular area extending from a central axis 420 of thepedestal 140/140A to a top surface diameter 422 that defines the edge ofthe central top surface. The electrically conductive layer 509 includesa plurality of wafer supports 404 a, 404 b, 404 c, 404 d, 404 e, and 404f, which are distributed across the electrically conductive layer 509and which are configured to support the wafer 101. A wafer support levelis defined by the vertical position of the bottom surface of the wafer101 when seated on the wafer supports 404 a, 404 b, 404 c, 404 d, 404 e,and 404 f. In the example of FIG. 4, there are six wafer supports 404 a,404 b, 404 c, 404 d, 404 e, and 404 f symmetrically distributed about aperiphery of the electrically conductive layer 509. However, in otherembodiments there may be any number of wafer supports on theelectrically conductive layer 509, and the wafer supports can bedistributed across the electrically conductive layer 509 in any suitablearrangement for supporting the wafer 101 during deposition processoperations.

In some embodiments, the electrically conductive layer 509 is notpresent on the central top surface of the pedestal 140/140A. And, inthese embodiments, the wafer supports 404 a, 404 b, 404 c, 404 d, 404 e,and 404 f are disposed on the central top surface of the pedestal140/140A. FIG. 4 also shows recesses 406 a, 406 b, and 406 c, which areconfigured to house lift pins. The lift pins can be utilized to raisethe wafer 101 from the wafer supports 404 a, 404 b, 404 c, 404 d, 404 e,and 404 f to allow for engagement of the wafer 101 by an end-effector.

In some embodiments, each wafer support 404 a, 404 b, 404 c, 404 d, 404e, and 404 f defines a minimum contact area structure (MCA). MCA's areused to improve precision mating between surfaces when high precision ortolerances are required, and/or minimal physical contact is desirable toreduce defect risk. Other surfaces in the system can also include MCA's,such as over the carrier ring 200 supports, and over the inner wafersupport region of the carrier ring 200.

The pedestal 140/140A further includes an annular surface 410 extendingfrom the top surface diameter 422 of the pedestal 140/140A to an outerdiameter 424 of the annular surface 410. The annular surface 410 definesan annular region surrounding the electrically conductive layer 509, butat a step down from the electrically conductive layer 509. That is, thevertical position of the annular surface 410 is lower than the verticalposition of the electrically conductive layer 509. A plurality ofcarrier ring supports 412 a, 412 b, and 412 c are positionedsubstantially at/along the edge (outer diameter) of the annular surface410 and are symmetrically distributed about the annular surface 410. Thecarrier ring supports can in some embodiments define MCA's forsupporting the carrier ring 200. In some implementations, the carrierring supports 412 a, 412 b, and 412 c extend beyond the outer diameter424 of the annular surface 410, whereas in other implementations they donot. In some implementations, the top surfaces of the carrier ringsupports 412 a, 412 b, and 412 c have a height that is slightly higherthan that of the annular surface 410, so that when the carrier ring 200is resting on the carrier ring supports 412 a, 412 b, and 412 c, thecarrier ring 200 is supported at a predefined distance above the annularsurface 410. Each carrier ring support 412 a, 412 b, and 412 c mayinclude a recess, such as recess 413 of carrier ring support 412 a, inwhich an extension protruding from the underside of the carrier ring 200is seated when the carrier ring 200 is supported by the carrier ringsupports 412 a, 412 b, and 412 c. The mating of the carrier ringextensions to the recesses (413) in the carrier ring supports 412 a, 412b, and 412 c provides for secure positioning of the carrier ring 200 andprevents the carrier ring 200 from moving when seated on the carrierring supports 412 a, 412 b, and 412 c.

In some implementations, the top surfaces of the carrier ring supports412 a, 412 b, and 412 c are flush with the annular surface 410. In otherimplementations, there are no carrier ring supports separately definedfrom the annular surface 410, so that the carrier ring 200 may restdirectly on the annular surface 410, and such that no gap exists betweenthe carrier ring 200 and the annular surface 410. In suchimplementations, a pathway between the carrier ring 200 and the annularsurface 410 is closed, preventing precursor materials from reaching abackside/underside of the wafer 101 via this pathway.

In the example embodiment of FIG. 4, there are three carrier ringsupports 412 a, 412 b, and 412 c positioned symmetrically along theouter edge region of the annular surface 410. However, in otherimplementations, there may be more than three carrier ring supports,distributed at any locations along the annular surface 410 of thepedestal 140/140A, to support the carrier ring 200 in a stable restingconfiguration.

When the wafer 101 is supported by the wafer supports 404 a, 404 b, 404c, 404 d, 404 e, and 404 f, and when the carrier ring 200 is supportedby the carrier ring supports 412 a, 412 b, and 412 c, an edge region ofthe wafer 101 is disposed over an inner portion of the carrier ring 200.Generally speaking, the edge region of the wafer 101 extends from anouter edge of the wafer 101 inward by about 2 millimeters (mm) to about5 mm. A vertical separation is thereby defined between the edge regionof the wafer 101 and the inner portion of the carrier ring 200. In someembodiments, this vertical separation is about 0.001 inch to about 0.010inch. The support of the carrier ring 200 at the predefined distanceabove the annular surface 410 and the vertical separation between theedge region of the wafer 101 and the inner portion of the carrier ring200, can be controlled to limit deposition on a backside/underside ofthe wafer 101 in the edge region of the wafer 101.

Some plasmas used to deposit thin films or to treat the wafer surfaceare unstable under conditions that are preferred from a processstandpoint. As an example, Ar/O2 capacitively-coupled-plasma (CCP)discharge operated within a 1 to 3 Torr pressure range and at high RFpower (>200 W per 300 mm diameter wafer processing station) showsinstabilities within the plasma. One such plasma instability, referredto herein as a “plasmoid,” is characterized by small areas of higherdensity (brighter) plasma surrounded by larger volumes of normal densityplasma. When plasmoids are formed, the deposited film is locallydensified near the plasmoid due to interaction of the film with thelocal high density plasma corresponding to the plasmoid, which resultsin degraded film uniformity. A spatial distribution of plasmoids overthe wafer 101 can vary from process-to-process, and within a givenprocess. Also, the plasmoids can move across the wafer 101 during agiven process. It should be understood that the plasmoids cause adegradation in process uniformity across the wafer 101, such as bychanging density and thickness of a deposited film at differentlocations across the wafer 101. The non-uniformity in film thicknesscaused by the plasmoids can be about 1% to 2% of the total filmthickness, which can be significant in some applications that require anultra-flat film profile.

During an example film deposition process, an operation is performed toapply a monolayer of a precursor gas, without applying any RF power. Theprecursor gas sticks to the wafer 101. In some embodiments, theprecursor gas includes silicon to enable formation of silicon oxide onthe wafer. An operation is then performed to flush the precursor gasfrom the processing volume over the wafer 101, thereby leaving themonolayer of the precursor gas on the wafer 101. An oxidation process isthen performed on the wafer 101. In the oxidation process, a process gasis flowed into the processing volume over the wafer 101 and RF power isapplied to the process gas to generate a plasma within the processingvolume. The plasma drives oxidation reactions on the wafer 101. In someembodiments, the process gas will contain oxygen plus one or more otherbombardment gases, such as argon, among others, where the bombardmentgas(es) provide sufficient densification of the plasma. In someembodiments, the bombardment gas is a gas that is effective indensifying a deposited film. Bombardment gases that densify thedeposited film are those gases that can effectively transfer energy tothe deposited film. In some embodiments, the bombardment gases aremonoatomic noble gases, such as argon, among others, that do not reactchemically with the deposited film and that lack vibrational orrotational molecular modes. For instance, in an example process, theprocess gas mixture can include about 5% to about 20% oxygen with thebalance of the process gas mixture being argon. And, in other exampleprocesses, the percentage of oxygen to the bombardment gas in theprocess gas mixture can be less than 5% or greater than 20%.

During the oxidation process, when a particular thickness of film isformed on the wafer 101, the plasmoids may begin to appear across thewafer 101. The number and size of the plasmoids has a direct correlationwith the amount of the bombardment process gas, e.g., argon, in theprocess gas mixture. So, reducing of the amount of bombardment processgas in the process gas mixture may serve to reduce the intensity of theplasmoids. However, the higher percentage of bombardment process gas isalso typically necessary to provide sufficient plasma density to ensureproper film formation. Also, a large amount of RF power is needed togenerate the plasma, because if there is not enough RF power applied,the plasma density will not be sufficient. However, increasing theapplied RF power leads to formation of more plasmoids. Some processapplications use about 300 W of applied RF power per 300 mm diameterwafer processing station. However, other process applications mayrequire higher RF power, such as 400 W, or even higher, per 300 mmdiameter wafer processing station.

In view of the foregoing, one approach for suppressing plasmoidformation is to reduce the applied RF power and/or increase the oxygenconcentration within the gas mixture. More specifically, lower processpower, i.e., lower applied RF power, or lower bombardment gas (typicallyargon) concentration within the process gas (with respect to oxygen)results in a lower plasma density, thus suppressing formation ofplasmoids. Unfortunately, these conditions are not preferred from adeposited film quality perspective. For example, film quality isdegraded when ion bombardment from the plasma is not sufficient at lowerprocess power or lower bombardment gas concentration within the processgas. Therefore, it may not always be possible to maintain deposited filmquality while suppressing plasmoid formation through lowering of theprocess power and/or lowering of the bombardment gas concentration,e.g., argon concentration, within the process gas.

Plasmoids may show up at the wafer 101 edge or close to the wafer 101center. Plasmoids can also move over the wafer 101 and create patternsof high intensity glow when several individual plasmoids merge intolarger ring-like structures. Due to the nature of the plasmoid, it isdifficult to control exactly when and where plasmoid formation willoccur over the wafer 101. Therefore, it is of interest to inhibitplasmoid formation without compromising on-wafer film thickness or otherproperties such as wet etch rate.

Energetic ions from the plasma may eject secondary electrons from thefilm material deposited on the wafer 101. These secondary electrons canbe accelerated to high energy when pulled into the bulk plasma throughthe plasma sheath. These accelerated electrons may form regions ofhigh-density, unstable plasma, such as the plasmoids. Such a behavior iscommonly observed in argon-rich gas mixtures when discharge interactswith specific surfaces (e.g., film of specific composition andthickness). Therefore, it has been determined that plasmoid formation isdependent to some degree on ion bombardment energy and/or ion energyflux.

PEALD is a process that deposits a film on the wafer in successivemonolayers. Each of these monolayers can be sensitive to ion bombardmentconditions as they are being deposited with a net effect on the finaldeposited film properties, such as density and/or thickness. In thisregard, PEALD processes have been observed to yield films withcharacteristics that depend on process variables known or believed tomodulate ion energy. This ion energy dependence may be tied to eitherpeak ion energy delivered or to the ion energy flux. Methods forproviding precise and separated control of ion energy and ion energyflux in the PEALD process can be useful for gaining access to a processspace that enables achievement of film qualities needed for fabricationof future advanced semiconductor device structures.

In addition to PEALD, there are other “continuous” deposition processesthat yield films with properties sensitive to ion bombardment energyand/or ion energy flux. In particular, the final film stress of nitridefilms deposited by PECVD can be dependent on the RF power levels of thelow frequency (LF) RF signals applied during processing. The RF powerlevel of the LF RF signals is believed to modulate ion energy. Also,other applications, such as amorphous hard mask (AHM) applications, canexhibit film stress and film density dependence on ion energy.

Some PEALD processes, such as those involving oxides, use a single highfrequency (HF) RF signal, such as 13.56 MHz in some embodiments, or27.12 MHz in other embodiments. In these PEALD processes the normallyavailable process variables, i.e., process parameters that can beadjusted to effect a change in the process results, include the HF RFpower, the chamber pressure, the composition of the process gas(es), andthe flow rate(s) of the process gas(es). The PEALD process has beenconventionally constrained within a process space/window defined bythese normally available process variables. However, as semiconductordevice structures continue to shrink in size and increase in designcomplexity, the process space/window defined by these normally availablePEALD process variables may not always be sufficient to yieldsatisfactory film deposition results.

In some PECVD processes, LF RF power (i.e., RF power at frequencies lessthan the system ion plasma frequency) is modulated to effect variationin deposited film properties that are believed to be dependent upon ionenergy within the plasma. However, use of LF RF power can suppressplasma density, and/or distort the uniformity of the plasma processacross the wafer, and/or increase the risk of electrical arcing withinthe chamber since the use of LF typically results in higher RF voltagesat the electrodes. Also, in some cases, LF RF power can couple with HFRF power to produce undesirable deposited film results. Therefore, whileuse of LF RF power modulation may assist with control of ion energydependent variations in deposited film properties, the use of LF RFpower modulation has some side-effects that can be prohibitive.

Given the issues discussed above with regard to how ion bombardmentenergy and/or ion energy flux affect film deposition results on thewafer in processes such as PEALD and PECVD, either through direct ioninteraction with the wafer or through formation of plasma instabilitiessuch as plasmoids, systems and methods are disclosed herein for usingthe electrical asymmetry effect (EAE) to separately modulate ion energyflux and peak ion energy in order to control variations in filmdeposition results caused by plasma ion behavior. EAE is a technique inwhich multiple RF generators operate simultaneously at frequencies in aharmonic relationship, and in which the multiple RF generators are phaselocked so as to operate at a specified phase angle relationship to eachother. In one example embodiment, EAE is utilized in a plasma depositionprocess by operating two RF generators in a simultaneous manner atfrequencies of 13.56 MHz and 27.12 MHz, respectively, and at a specificphase angle relationship to each other. It should be understood that inother embodiments more than two RF generators can be operated atrespective frequencies having a harmonic relationship, and therespective frequencies can be different than 13.56 MHz and 27.12 MHz.Also, variation/control of the phase angle relationship between themultiple RF generators in the EAE-enabled plasma deposition process canbe used to suppress plasma instability formation, such as plasmoidformation, and can provide for control of ALD-oxide film density, andcan provide for control of film stress in PECVD deposition of nitrides.It should also be understood that use of EAE along withvariation/control of its associated phase angle relationships canprovide other plasma deposition process benefits, and serves to expandthe effective process space/window of PECVD and PEALD plasma depositionprocesses.

FIG. 5 shows a plasma processing system configured to implement EAEcontrol to provide for separate modulation of ion energy flux and peakion energy in order to control variations in film deposition resultscaused by plasma ion behavior, in accordance with some embodiments ofthe present invention. The system of FIG. 5 includes the chamber 102 andcorresponding components as described with regard to either FIG. 1A orFIG. 1B. In some embodiments, the system of FIG. 5 includes theshowerhead electrode 150 and pedestal 140 as described with regard toFIG. 1A. And, in some embodiments, the system of FIG. 5 includes theshowerhead electrode 150A and pedestal 140A as described with regard toFIG. 1B. The system of FIG. 5 includes an RF power supply 104A connectedto supply RF power to the showerhead electrode 150/150A. The RF powersupply 104A is also connected to receive control signals from thecontrol module 110. In the system of FIG. 5, the RF electrode 254 withinthe pedestal 140A and/or the pedestal 140 is electrically connected to areference ground potential.

The RF power supply 104A includes multiple, i.e., an integer number Ngreater than 1, RF generators 501(1)-501(N). Each RF generator501(1)-501(N) is configured to output RF signals of a prescribedfrequency. And, each RF generator 501(1)-501(N) is independentlycontrollable, such that the prescribed RF signal frequency output by agiven one of the RF generators 501(1)-501(N) can be different than theRF signal frequency output by others of the RF generators 501(1)-501(N).Each RF generator 501(1)-501(N) is connected to a phase controller 503.The phase controller 503 is configured to control a phase anglerelationship between RF signals output by the RF generators501(1)-501(N). More specifically, the phase controller 503 is configuredto establish a prescribed phase angle relationship between RF signalsoutput by any two of the RF generators 501(1)-501(N), and maintain thatestablished prescribed phase angle relationship as long as needed duringthe plasma deposition process. Also, the phase controller 503 isconfigured to provide for controlled adjustment of any prescribed phaserelationship between RF signals output by any two of the RF generators501(1)-501(N) during the plasma deposition process. In this manner, thephase controller 503 and the multiple RF generators 501(1)-501(N)provide additional process variables to expand the process space/windowof the plasma deposition process, including of a number (greater than 1)of RF signal frequencies applied, a value of each RF signal frequencyapplied, an amplitude of each RF signal applied, and a phase anglerelationship between each RF signal applied.

Each RF generator 501(1)-501(N) is connected to output the RF signalsthat it generates to a corresponding one of multiple match networks106(1)-106(N). Each of the multiple match networks 106(1)-106(N) isconfigured to control impedance matching so that the RF signalsgenerated by the corresponding RF generator 501(1)-501(N) can betransmitted effectively to the plasma load within the chamber 102.Generally speaking, each of the multiple match networks 106(1)-106(N)includes matching circuitry configured as a network of capacitors andinductors that can be adjusted to tune impedance encountered by the RFsignals in their transmission to the plasma load within the chamber 102.

Each of the multiple match networks 106(1)-106(N) has a respectiveoutput connected to a combiner module 507. In some embodiments, thecombiner module 507 includes multiple notch filters 505(1)-505(N), witheach notch filter 505(1)-505(N) connected to receive RF signals from acorresponding one of the match networks 106(1)-106(N). It should beunderstood that in some embodiments each notch filter 505(1)-505(N) canactually include multiple notch filters. Each of the notch filters505(1)-505(N) is configured to reduce/eliminate signals outside of anarrow range of frequency. The notch filter 505(1)-505(N) correspondingto a given RF generator 501(1)-501(N) is configured to reduce/eliminateRF signals at frequencies of the other RF generators 501(1)-501(N). Forexample, the notch filter 505(1) corresponding to the RF generator501(1) is configured to reduce/eliminate RF signals at frequenciesoutput by the other RF generators 501(2)-501(N), and the notch filter505(2) corresponding to the RF generator 501(2) is configured toreduce/eliminate RF signals at frequencies output by the other RFgenerators 501(1) and 501(3)-501(N), and so on. In this manner, thecombiner 507 functions to combine cleaned versions of each RF signal asoutput from each match network 106(1)-106(N) associated with each RFgenerator 501(1)-501(N) onto a single output line 509 for transmissionto the showerhead electrode 150/150A within the chamber 102. Also, insome embodiments, lengths of transmission lines 511(1)-511(N) extendingfrom the outputs of the various notch filters 505(1)-505(N) to thesingle output line 509 can be individually varied to enable independentload impedance optimization for each RF signal frequency. Also, itshould be understood that in some embodiments, the combiner module 507can be configured to combine cleaned versions of each RF signal asoutput from each match network 106(1)-106(N) associated with each RFgenerator 501(1)-501(N) onto the single output line 509 using filtercircuits other than the notch filters 505(1)-505(N). For example, in thecase of two RF signal frequencies, an arrangement of one or more highpass filters and one or more low pass filters can be used to providefrequency-cleaned versions of the two RF signals to the single outputline 509.

FIG. 6 shows another plasma processing system configured to implementEAE control to provide for separate modulation of ion energy flux andpeak ion energy in order to control variations in film depositionresults caused by plasma ion behavior, in accordance with someembodiments of the present invention. In the system of FIG. 6, the RFpower supply 104A is connected to supply RF signals to the RF electrode254 within the pedestal 140/140A, and the showerhead electrode 150/150Ais electrically connected to a reference ground potential. The RF powersupply 104A shown in FIG. 6 is the same as that described with regard toFIG. 5.

FIG. 7 shows another plasma processing system configured to implementEAE control to provide for separate modulation of ion energy flux andpeak ion energy in order to control variations in film depositionresults caused by plasma ion behavior, in accordance with someembodiments of the present invention. The system of FIG. 7 implementsthe RF direction control module 250 as described with regard to FIGS. 1Aand 1B. In some embodiments, the RF direction control module 250 isconnected between the RF power supply 104A and both the RF electrode 254within the pedestal/pedestal 140/140A and the showerhead electrode150/150A to provide for operation of either the RF electrode 254 withinthe pedestal/pedestal 140/140A or the showerhead electrode 150/150A asthe RF supply electrode at a given time, while the other of the RFelectrode 254 within the pedestal/pedestal 140/140A and the showerheadelectrode 150/150A is operated as the RF return electrode, i.e.,reference ground electrode, at the given time.

The multiple (N>1) RF generators 501(1)-501(N) of the RF power supply104A are set to operate at N frequencies, where a lowest of the Nfrequencies is a base frequency, i.e., fundamental frequency, and whereeach of the N frequencies that is greater than the base frequency is aneven harmonic of the base frequency. And, the phase controller 503operates to establish and control a phase angle relationship, i.e., RFvoltage phase relationship, between the RF signals generated by the RFgenerators 501(1)-501(N). The phase angle relationship between the RFsignals generated by the RF generators 501(1)-501(N) is deterministicand adjustable under the control of the phase controller 503. Variationof the phase angle relationship between the RF signals generated by theRF generators 501(1)-501(N) provides for variation of both directcurrent (DC) self bias and plasma potential, and in turn provides forvariation in ion energy incident upon the wafer.

It should be understood that the RF power supply 104A can include anynumber N of RF generators 501(1)-501(N), where N is greater than 1.However, in some embodiments, the RF power supply 104A is configured toinclude two RF generators 501(1) and 501(2), i.e., N=2. And, theseembodiments, the RF power supply 104A includes two match networks 106(1)and 106(2), and includes two notch filters 505(1) and 505(2), inaddition to the phase controller 503, such as shown in FIGS. 5, 6, and7. It should also be understood that each of the RF generators501(1)-501(N) can be set to operate at essentially any frequency, solong as each of the different frequencies of the RF generators501(1)-501(N) that is greater than the base frequency is an evenharmonic of the base frequency. When an even integer harmonicrelationship exists between a higher frequency and the base frequency,the higher frequency is an even integer multiple of the base frequency.

In some embodiments, a first RF generator 501(1) of the two RFgenerators in the above-mentioned embodiment is set to generate RFsignals at a frequency of 13.56 MHz, and a second RF generator 501(2) ofthe two RF generators in the above-mentioned embodiment is set togenerate RF signals at a frequency of 27.12 MHz, such that the eveninteger harmonic relationship of 2 exists between these two frequencies.

In the above-mentioned embodiment in which the two RF generators 501(1)and 501(2) are set to operate at frequencies of 13.56 MHz and 27.12 MHz,respectively, the power electrode voltage (V_(electrode)(t)) is given byEquation 1, where A_(13.56) is the amplitude of the 13.56 MHz frequencyRF signal, f_(13.56) is the frequency of 13.56 MHz, A_(27.12) is theamplitude of the 27.12 MHz frequency RF signal, f_(27.12) is thefrequency of 27.12 MHz, t is time, and φ is the EAE phase anglerelationship between the 13.56 MHz and 27.12 MHz RF signals.V _(electrode)(t)=A _(13.56) sin(2πf _(13.56) t+φ)+A _(27.12) sin(4πf_(27.12) t)  Equation 1.

In using the above-mentioned embodiment in which the two RF generators501(1) and 501(2) are set to operate at frequencies of 13.56 MHz and27.12 MHz, respectively, to perform a PEALD-oxide film depositionprocess, the powered electrode voltage demonstrates good sinusoidalmodulation with adjustment in the EAE phase angle relationship betweenthe two RF signals. The modulation of powered electrode voltageindicates a minima near an EAE phase angle relationship of about 10° anda maxima near an EAE phase angle relationship of about 55°.

To explore the performance of this embodiment, a first wafer wassubjected to the PEALD-oxide film deposition process using the EAE phaseangle relationship of about 10°, and a second wafer was subjected to thePEALD-oxide film deposition process using the EAE phase anglerelationship of about 55°. During the process using the EAE phase anglerelationship of about 10°, no plasmoids were observed throughout thedeposition process. However, during the process using the EAE phaseangle relationship of about 55°, plasmoids appeared, i.e., turned on, atabout cycle 50 and remained on for the duration of the process, which issimilar to the plasmoid behavior observed using only RF signals of 13.56MHz. In view of these results, it is demonstrated that plasmoids can becontrolled, i.e., turned on and off, through modulation (controlledvariation) of the EAE phase angle relationship.

FIG. 8 shows plots of deposited film thickness profile across the wafercorresponding to use of the EAE phase angle relationship of about 10°and corresponding to use of the EAE phase angle relationship of about55°, in accordance with some embodiments of the present invention. Asshown in FIG. 8, the process using the EAE phase angle relationship ofabout 10° had a lower film deposition rate than the process using theEAE phase angle relationship of about 55°. Also, FIG. 8 shows anaberration in deposited film thickness below location point 10 with useof the EAE phase angle relationship of about 55°, which is indicative ofplasmoids present during the deposition process. In contrast, FIG. 8shows no aberration in deposited film thickness across the profile withuse of the EAE phase angle relationship of about 10°, which isindicative of no plasmoid formation during the deposition process.

Additionally, it was determined that the deposition process using theEAE phase angle relationship of about 10° provided a greater filmdensity as compared to that obtained using the EAE phase anglerelationship of about 55°, which is indicative of a lower wet etch rate(WER) with lower EAE phase angle relationship. Therefore, it has beendemonstrated that by using of a lower EAE phase angle relationship it ispossible to obtain a denser deposited film through generation of ahigher density plasma in conjunction with a lower wafer bias and noplasmoid formation. Use of only a single RF frequency of 27.12 MHz didnot provide for a denser deposited film through generation of a higherdensity plasma in conjunction with a lower wafer bias and no plasmoidformation. Also, based on deposition rate trends, use of only a singleRF frequency of 27.12 MHz may provide a higher plasma density and alower wafer bias as compared to use of only a single RF frequency of13.56 MHz, but the film deposition rate using only the single RFfrequency of 27.12 MHz is higher for a given power as compared to use ofonly the single RF frequency of 13.56 MHz.

With respect to PECVD, it was determined that the film stress of nitridefilms can be varied as the EAE phase angle relationship is varied. Thisdependence of film stress on the EAE phase angle relationship opens upan available process space/window for film deposition processes andprovides for process and film characteristics that have been previouslyunattainable. More specifically, the methods and systems disclosedherein for simultaneously using multiple RF signal frequencies (where alowest of the multiple RF signal frequencies is a base frequency, i.e.,fundamental frequency, and where each radiofrequency signal having afrequency greater than the base frequency is in an even harmonicrelationship with the radiofrequency signal of the base frequency, andwhere each radiofrequency signal having a frequency greater than thebase frequency is in a fixed phase relationship with the radiofrequencysignal of the base frequency) to generate the plasma for a filmdeposition process, in conjunction with controlled variation of the EAEphase angle relationship(s) between the multiple RF signal frequencies,expands the available process space/window available for both PEALD andPECVD processes by enabling separate control of ion energy and ionenergy flux, and by providing for suppression of plasmoid formation.

In view of the foregoing, it should be understood that a system forperforming a plasma process to deposit a film on a wafer is disclosedherein. The system includes a pedestal (140/140A) having a top surfaceconfigured to support a wafer (101). The system also includes a plasmageneration region formed above the top surface of the pedestal(140/140A). The system also includes a process gas supply configured tosupply a process gas composition to the plasma generation region. Theprocess gas composition includes oxygen and at least one bombardmentgas, where the at least one bombardment gas is effective in densifyingthe film deposited on the wafer. The system also includes an electrode(150/150A/254) disposed in proximity to the plasma generation region toprovide for transmission of radiofrequency signals from the electrode(150/150A/254) into the plasma generation region. The system alsoincludes a radiofrequency power supply (104A) configured tosimultaneously supply multiple radiofrequency signals of differentfrequencies to the electrode (150/150A/254). A lowest of the differentfrequencies is a base frequency, i.e., fundamental frequency, and eachradiofrequency signal having a frequency greater than the base frequencyis in an even harmonic relationship with the radiofrequency signal ofthe base frequency, and where each radiofrequency signal having afrequency greater than the base frequency is in a fixed phaserelationship with the radiofrequency signal of the base frequency. Themultiple radiofrequency signals have respective frequencies set totransform the process gas composition into the plasma within the plasmageneration region to cause deposition of the film on the wafer. Theradiofrequency power supply (104A) also includes a phase controllerconfigured to provide for variable control of a phase angle relationshipbetween each of the multiple radiofrequency signals to control aparameters of the film deposited on the wafer. In various embodiments,the parameter of the film that is controlled by controlling the phaseangle relationship between the multiple radiofrequency signals includesone or more of a density of the film, a stress of the film, a refractiveindex of the film, and a content of a minority material specie withinthe film, among other film parameters. Also, in some embodiments, thephase controller provides for adjustment of the phase angle relationshipbetween the multiple radiofrequency signals to suppress plasmoidformation within the plasma.

The radiofrequency power supply (104A) includes multiple radiofrequencysignal generators (501(1)-501(N)) for respectively generating each ofthe multiple radiofrequency signals. The radiofrequency power supply(104A) also includes a phase controller (503) connected to each of themultiple radiofrequency signal generators (501(1)-501(N)). The phasecontroller (503) is configured to provide for variable control of phaseangle relationship between any pair of the multiple radiofrequencysignals respectively generated by the multiple radiofrequency signalgenerators (501(1)-501(N)).

The radiofrequency power supply (104A) also includes multiple matchnetworks (106(1)-106(N)) respectively connected to outputs of themultiple radiofrequency signal generators (501(1)-501(N)), such thateach of the multiple radiofrequency signal generators (501(1)-501(N)) isconnected to a separate one of the multiple match networks(106(1)-106(N)). The radiofrequency power supply also includes acombiner module (507) having inputs connected to outputs of the multiplematch networks (106(1)-106(N)). The combiner module (507) is configuredto combine clean versions of each of the multiple radiofrequency signalsas output from the multiple match networks (106(1)-106(N)) correspondingto the multiple radiofrequency signal generators (501(1)-501(N)) onto asingle output line (509) of the combiner module (507) for transmissionto the electrode (150/150A/254).

In some embodiments, the combiner module (507) includes multiple notchfilters (505(1)-505(N)), with each of the multiple notch filters(505(1)-505(N)) connected to receive radiofrequency signals from acorresponding one of the multiple match networks (106(1)-106(N)). Eachof the multiple notch filters (505(1)-505(N)) is configured to reduceand/or eliminate signals outside of a narrow range of frequency. Theoutputs of the multiple notch filters (505(1)-505(N)) are connected tothe single output line (509) of the combiner module (507).

Any given one of the multiple notch filters (505(1)-505(N)) isconfigured to pass signals corresponding to the frequency of theparticular one of the multiple radiofrequency signal generators(501(1)-501(N)) to which the given one of the multiple notch filters(505(1)-505(N)) is connected by way of its corresponding one of themultiple match networks (106(1)-106(N)). And, the given one of themultiple notch filters (505(1)-505(N)) is configured to reduce and/oreliminate signals having frequencies corresponding to others of themultiple radiofrequency signal generators (501(1)-501(N)) different thanthe particular one of the multiple radiofrequency signal generators(501(1)-501(N)) to which the given one of the multiple notch filters(505(1)-505(N)) is connected by way of its corresponding one of themultiple match networks (106(1)-106(N)). In some embodiments, each ofthe multiple notch filters (505(1)-505(N)) includes multiple notchfilters (505(1)-505(N)) within itself. Also, it should be understoodthat in some embodiments, the combiner module (507) can be configured touse filter circuits other than the notch filters (505(1)-505(N)). Forexample, in some embodiments, the combiner module (507) is configured touse an arrangement of one or more high pass filters and one or more lowpass filters instead of notch filters or in combination with notchfilters.

In some embodiments, the combiner module (507) includes separatetransmission lines (511(1)-511(N)) disposed to respectively connect theoutputs of the multiple notch filters (505(1)-505(N)) to the singleoutput line (509) of the combiner module (507). And, each of theseparate transmission lines (511(1)-511(N)) has an individuallyprescribed length to enable independent load impedance optimization fora particular radiofrequency signal frequency.

In some embodiments, the electrode (150/150A) is positioned over theplasma generation region, and the pedestal (140/140A) includes a groundelectrode electrically connected to a reference ground potential, suchas shown in FIG. 5. In some embodiments, the electrode (254) ispositioned within the pedestal (140A) or the pedestal (140) itselfserves as the electrode, and the system includes a ground electrode(150/150A) positioned over the plasma generation region, with the groundelectrode (150/150A) electrically connected to a reference groundpotential, such as shown in FIG. 6.

FIG. 9 shows a flowchart of a method for performing a plasma process todeposit a film on a wafer, in accordance with some embodiments of thepresent invention. In some embodiments, the plasma process is a PEALDprocess. In some embodiments, the plasma process is a PECVD process. Themethod includes an operation 901 for positioning a wafer on a topsurface of a pedestal in exposure to a plasma generation region. Themethod also includes an operation 903 for supplying a process gascomposition to the plasma generation region. The process gas compositionincludes oxygen and at least one bombardment gas. In some embodiments,the at least one bombardment gas is effective in densifying the filmdeposited on the wafer. In some embodiments, the at least onebombardment gas includes a monoatomic noble gas. In some embodiments,the at least one bombardment gas lacks vibrational or rotationalmolecular modes. In some embodiments, the at least one bombardment gasis argon.

The method also includes an operation 905 for generating radiofrequencysignals of at least two different frequencies. A lowest of the at leasttwo different frequencies is a base frequency, i.e., fundamentalfrequency, and each radiofrequency signal having a frequency greaterthan the base frequency is in an even harmonic relationship with theradiofrequency signal of the base frequency, and where eachradiofrequency signal having a frequency greater than the base frequencyis in a fixed phase relationship with the radiofrequency signal of thebase frequency. The method also includes an operation 907 for supplyingthe generated radiofrequency signals to an electrode for transmissioninto the plasma generation region. The radiofrequency signals transformthe process gas composition into a plasma within the plasma generationregion, and the plasma causes deposition of the film on the wafer. Themethod also includes an operation 909 for adjusting a phase anglerelationship between radiofrequency signals of each of the at least twodifferent frequencies to control a parameter of the film deposited onthe wafer. In some embodiments, the parameter of the film that iscontrolled by adjusting the phase angle relationship betweenradiofrequency signals in operation 909 includes one or more of adensity of the film, a stress of the film, a refractive index of thefilm, and a content of a minority material specie within the film, amongother film parameters. For example, with regard to controlling thecontent of a minority material specie within the film, in someembodiments the minority material specie may be hydrogen, with ionbombardment on the film removing hydrogen from the film. And, in theseembodiments, the phase angle relationship between radiofrequency signalsof each of the at least two different frequencies can be adjusted tocontrol ion bombardment on the film, which in turn controls the hydrogencontent within the film. It should be understood that control ofhydrogen content within the film is one of many examples of how thephase angle adjustment of operation 909 can be used to control thecontent of a minority material specie within the film. Also, in someembodiments, adjusting the phase angle relationship betweenradiofrequency signals of each of the at least two different frequenciesin operation 909 is performed to suppress plasmoid formation within theplasma. And, such suppression of plasmoid formation can be achieved inconjunction with control of a given parameter of the deposited film.

The method can also include providing a separate impedance matching foreach of the generated radiofrequency signals. And, the method caninclude combining the radiofrequency signals of at least two differentfrequencies onto a single output line for transmission to the electrode.In some embodiments, combining the radiofrequency signals includesprocessing each of the radiofrequency signals to filter out signals offrequency different than that of the processed radiofrequency signalprior to transmission of the processed radiofrequency signal to thesingle output line.

In some embodiments, generating radiofrequency signals of at least twodifferent frequencies in operation 903 includes generating a firstradiofrequency signal having a frequency of about 13.56 MHz andgenerating a second radiofrequency signal having a frequency of about27.12 MHz. And, in these embodiments controlling the phase anglerelationship between radiofrequency signals of each of the at least twodifferent frequencies in operation 905 includes controlling a phaseangle relationship between the first radiofrequency signal and thesecond radiofrequency signal to be about 10 degrees. It should beunderstood, however, that in other embodiments the method of FIG. 9 caninclude generating radiofrequency signals of frequencies other than13.56 MHz and 27.12 MHz, and can include controlling the phase anglerelationship at other than 10 degrees.

The systems and methods disclosed herein for controlling EAE phase anglerelationship between radiofrequency signals of different frequency areeffective in controlling film densification and in suppressing plasmoidformation during various plasma-enhanced deposition processes, such asPEALD and PECVD processes. However, it should also be understood thatthe systems and methods disclosed herein for controlling EAE phase anglerelationship between radiofrequency signals of different frequencyprovides for separation of ion energy control from plasma densitycontrol in many different plasma-enhanced film deposition processes. Thesystems and methods disclosed herein provide for control of essentiallyany process film parameter that is dependent on ion energy by use of aphase angle adjustment rather than by a change in the total powerapplied to the plasma. This control of process film parameter(s) byphase angle adjustment rather than by total power adjustment can beutilized in essentially any plasma-based film deposition process. Forexample, fabrication of some semiconductor devices, such as VNANDdevices, require deposition of a large number of successive films(perhaps 50 or more) of alternating materials, such as oxide andnitride, where each film layer needs to be stress tuned so that theoverall film stack satisfies a given film stress specification. In suchembodiments, the systems and methods disclosed herein for using phaseangle adjustment to control ion energy separate from plasma density canbe used to control the stress of each deposited film layer based on thespecific characteristics of that deposited film layer. It should beunderstood that the systems and methods disclosed herein for using phaseangle adjustment to control ion energy separate from plasma density canbe used to control essentially any parameter of a deposited film that isdependent on ion energy.

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications can be practiced within the scope of theappended claims. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the invention is notto be limited to the details given herein, but may be modified withinthe scope and equivalents of the described embodiments.

What is claimed is:
 1. A method for performing a plasma process to deposit a film on a wafer, comprising: positioning the wafer on a top surface of a pedestal in exposure to a plasma generation region; supplying a process gas composition to the plasma generation region, the process gas composition including oxygen and at least one bombardment gas; generating radiofrequency signals of at least two different frequencies, wherein a lowest of the at least two different frequencies is a base frequency, and wherein each radiofrequency signal having a frequency greater than the base frequency is in an even harmonic relationship with the radiofrequency signal of the base frequency, and wherein each radiofrequency signal having a frequency greater than the base frequency is in a fixed phase relationship with the radiofrequency signal of the base frequency; supplying the generated radiofrequency signals to an electrode for transmission into the plasma generation region, the radiofrequency signals transforming the process gas composition into a plasma within the plasma generation region, the plasma causing deposition of the film on the wafer; and adjusting a phase angle relationship between radiofrequency signals of each of the at least two different frequencies to control a parameter of the film deposited on the wafer.
 2. The method as recited in claim 1, further comprising: providing a separate impedance matching for each of the generated radiofrequency signals.
 3. The method as recited in claim 2, further comprising: combining the radiofrequency signals of at least two different frequencies onto a single output line for transmission to the electrode.
 4. The method as recited in claim 3, wherein combining the radiofrequency signals includes processing each of the radiofrequency signals to filter out signals of frequency different than that of the processed radiofrequency signal prior to transmission of the processed radiofrequency signal to the single output line.
 5. The method as recited in claim 4, wherein generating radiofrequency signals of at least two different frequencies includes generating a first radiofrequency signal having a frequency of about 13.56 MHz and generating a second radiofrequency signal having a frequency of about 27.12 MHz, and wherein controlling the phase angle relationship between radiofrequency signals of each of the at least two different frequencies includes controlling a phase angle relationship between the first radiofrequency signal and the second radiofrequency signal.
 6. The method as recited in claim 1, wherein the at least one bombardment gas includes a monoatomic noble gas.
 7. The method as recited in claim 6, wherein the at least one bombardment gas lacks vibrational or rotational molecular modes.
 8. The method as recited in claim 1, wherein the at least one bombardment gas is argon.
 9. The method as recited in claim 1, wherein the plasma process is a plasma enabled atomic layer deposition process.
 10. The method as recited in claim 1, wherein the plasma process is a plasma enabled chemical vapor deposition process.
 11. The method as recited in claim 1, wherein the parameter of the film that is controlled by adjusting the phase angle relationship between radiofrequency signals of each of the at least two different frequencies includes one or more of a density of the film, a stress of the film, a refractive index of the film, and a content of a minority material specie within the film.
 12. The method as recited in claim 1, wherein adjusting the phase angle relationship between radiofrequency signals of each of the at least two different frequencies is performed to suppress plasmoid formation within the plasma.
 13. The method as recited in claim 1, wherein the at least one bombardment gas is effective in densifying the film deposited on the wafer.
 14. A system for performing a plasma process to deposit a film on a wafer, comprising: a pedestal having a top surface configured to support the wafer; a plasma generation region formed above the top surface of the pedestal; a process gas supply configured to supply a process gas composition to the plasma generation region, the process gas composition including oxygen and at least one bombardment gas; an electrode disposed in proximity to the plasma generation region to provide for transmission of radiofrequency signals from the electrode into the plasma generation region; and a radiofrequency power supply configured to simultaneously supply multiple radiofrequency signals of different frequencies to the electrode, wherein a lowest of the different frequencies is a base frequency, and wherein each radiofrequency signal having a frequency greater than the base frequency is in an even harmonic relationship with the radiofrequency signal of the base frequency, and wherein each radiofrequency signal having a frequency greater than the base frequency is in a fixed phase relationship with the radiofrequency signal of the base frequency, the multiple radiofrequency signals having respective frequencies set to transform the process gas composition into the plasma within the plasma generation region to cause deposition of the film on the wafer, the radiofrequency power supply also including a phase controller configured to provide for variable control of a phase angle relationship between each of the multiple radiofrequency signals, wherein adjustment of the phase angle relationship is used to control a parameter of the film deposited on the wafer.
 15. The system as recited in claim 14, wherein the radiofrequency power supply includes multiple radiofrequency signal generators for respectively generating each of the multiple radiofrequency signals.
 16. The system as recited in claim 15, wherein the phase controller is connected to each of the multiple radiofrequency signal generators, the phase controller configured to provide for variable control of phase angle relationship between any pair of the multiple radiofrequency signals respectively generated by the multiple radiofrequency signal generators.
 17. The system as recited in claim 15, wherein the radiofrequency power supply includes multiple match networks respectively connected to outputs of the multiple radiofrequency signal generators, such that each of the multiple radiofrequency signal generators is connected to a separate one of the multiple match networks.
 18. The system as recited in claim 17, wherein the radiofrequency power supply includes a combiner module having inputs connected to outputs of the multiple match networks, the combiner module configured to combine clean versions of each of the multiple radiofrequency signals as output from the multiple match networks corresponding to the multiple radiofrequency signal generators onto a single output line of the combiner module for transmission to the electrode.
 19. The system as recited in claim 18, wherein the combiner module includes multiple notch filters, with each of the multiple notch filters connected to receive radiofrequency signals from a corresponding one of the multiple match networks, wherein each of the multiple notch filters is configured to reduce and/or eliminate signals outside of a narrow range of frequency, and wherein outputs of the multiple notch filters are connected to the single output line of the combiner module.
 20. The system as recited in claim 19, wherein any given one of the multiple notch filters is configured to pass signals corresponding to the frequency of the particular one of the multiple radiofrequency signal generators to which the given one of the multiple notch filters is connected by way of its corresponding one of the multiple match networks, and wherein the given one of the multiple notch filters is configured to reduce and/or eliminate signals having frequencies corresponding to others of the multiple radiofrequency signal generators different than the particular one of the multiple radiofrequency signal generators to which the given one of the multiple notch filters is connected by way of its corresponding one of the multiple match networks.
 21. The system as recited in claim 20, wherein each of the multiple notch filters includes multiple notch filters.
 22. The system as recited in claim 19, wherein the combiner module includes separate transmission lines disposed to respectively connect the outputs of the multiple notch filters to the single output line of the combiner module, and wherein each of the separate transmission lines has an individually prescribed length to enable independent load impedance optimization for a particular radiofrequency signal frequency.
 23. The system as recited in claim 14, wherein the electrode is positioned over the plasma generation region, and wherein the pedestal includes a ground electrode electrically connected to a reference ground potential.
 24. The system as recited in claim 14, wherein the electrode is positioned within the pedestal, and wherein the system includes a ground electrode positioned over the plasma generation region, the ground electrode electrically connected to a reference ground potential. 